VERY-LOW FRUIT - FLOWER RATIOS IN GREVILLEA (PROTEACEAE) ARE INDEPENDENT OF BREEDING SYSTEM

Members of the family Proteaceae have extremely low mature fruit:flowe r (FR:FL) ratios (range 0.001-0.163) compared with other temperate, he rmaphroditic, woody perennials. Sutherland's (1986) survey of FR:FL ra tios indicated that compatibility was an important factor explaining l evels of fruit set. The role of compatibility in regulating FR:FL rati os was tested in five closely related species of Grevillea (Proteaceae ). Species-specific compatibility was compared using the self-compatib ility index (SI = ratio of selfed fruit set to crossed fruit set) calc ulated at fruit initiation to minimise the confounding effect of other post-fertilisation fruit losses, such as inbreeding depression and pr e-dispersal predation. Fruit:flower ratios at initiation ranged from 0 .041-0.249, and at maturity 0.015-0.096. Grevillea species showed high ly variable breeding systems: G. linearifolia was self-incompatible (S I = 0.003), G. sphacelata, G. mucronulata, and G. oleoides were partia lly self-compatible (SI = 0.07-0.28) and G. longifolia was self-compat ible (SI = 0.61). Intrapopulation variability in the level of self-inc ompatibility was high in all species but G. linearifolia. The correlat ion between SI and FR:FL ratios was non-significant, indicating that c ompatibility has a minimal effect on fruit set in the Grevillea specie s studied, and that these data, together with other data on proteaceou s species do not support trends observed in Sutherland's survey. Low F R:FL ratios resulted from of a combination of pollen limitation, and h igh levels of flower and fruit predation.